Grain-boundary states in solid oxide electrolyte ceramics processed using iron oxide sintering aids: a Mössbauer spectroscopy study

• Published in: Journal of solid state electrochemistry Vol. 21; no. 10; pp. 2965 - 2974
• Main Authors: Tsipis, E.V., Waerenborgh, J.C., Kharton, V.V.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.10.2017; Springer Nature B.V
• Subjects: Additives; Analytical Chemistry; Cations; Ceramics; Cerium oxides; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Densification; Disproportionation; Ductile-brittle transition; Electrochemistry; Electrolytes; Electron transport; Energy Storage; Fluorite; Fracture mechanics; Hematite; Iron oxides; Lanthanum; Lattices; Original Paper; Physical Chemistry; Sintering aids; Solid electrolytes; Spectrum analysis; Yttria-stabilized zirconia; Yttrium oxide; Zirconium dioxide; YSZ; Solid oxide electrolyte ceramics; Sintering aid; LSGM; Mössbauer spectroscopy; Doped ceria
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-017-3622-3

In order to appraise microstructure-determined defect formation processes and minor intergranular states in the solid electrolyte materials sintered employing transition metal oxide additives, the transmission Mössbauer spectroscopy analysis of Zr 0.85 Y 0.15 O 2 − δ , Ce 0.9 Gd 0.1 O 2 − δ , and (La 0.9 Sr 0.1 ) 0.98 Ga 0.8 Mg 0.2 O 3 − δ ceramics containing 2 mol% 57 Fe isotope probe was combined with X-ray diffraction and scanning electron microscopy studies. The sintering aids tend to dissolve in yttria-stabilized zirconia and lanthanum gallate where Fe-rich domains, magnetically ordered at 4 K, co-exist with interfacial iron species remaining paramagnetic. For the electrolyte ceramics processed at 1373 K, this dissolution is accompanied with an appearance of insulating phase impurities, such as monoclinic zirconia. On the contrary, low iron solubility in gadolinia-doped ceria leads to the segregation of trace amounts of hematite and perovskite-type GdFeO 3 phases, which enhance densification and affect p-type electronic transport. The iron cations incorporated into the fluorite-type cubic zirconia and ceria lattices are predominantly trivalent, with reduced oxygen coordination relative to the host cations, while the Fe 4+ states prevailing in the gallate ceramics sintered in air exhibit atypical disproportionation into Fe 3+ and Fe 5+ even at room temperature.